For volume measurement of flowing fluid it is known to use a rotor with blades mounted in a housing, which blades are pivotally connected with a rotor body and which are forcibly guided in such a way that over one part of the cylindrical wall of the housing they are turned towards this to form a barrier between the inlet and outlet port, and over another part of the cylindrical wall of the housing having a smaller diameter than the former they are deflected backwards relative to the rotating direction to form a sealing between this part of the cylindrical wall and the rotor. The known devices of this kind, e.g. water meters, are relatively expensive to produce and repair, the blades being difficult to exchange piece by piece, for which reason it is often necessary to exchange the whole rotor. In many cases the rotor provides an undesired, great resistance against rotation, too. Yet another drawback of some of the known liquid meters is that the pivotally connected blades have a tendency to stick when the device has not been used for a longer period of time, and that they are noise generating.
However, from U.S. Pat. No. 2,753,809 a motor or pump is known, the rotor of which is provided with blades where a metal plate is mounted along the flexible elastomeric blade part to reinforce this part which is constituted by an extending tab on an elastomeric base embedded in a groove in the rotor. By this construction a relatively great amount of elastomeric material for each blade is involved, and in connection with abrasion of the material it is necessary to renew the whole blade.
Besides, from U.S. Pat. Nos. 2,636,478 and 2,636,479 liquid meters are known where wings of flexible material are extending practically from the center of the hub to the circumference and which are supported by intricately constructed metal parts. Also by this construction it is difficult to exchange worn parts piece by piece, and furthermore, the wings, which slide against the wall of the housing, involve a relatively great resistance against the movement of the rotor in the housing.